Construction material composition and method of forming construction materials utilizing rice hulls

ABSTRACT

Provided are a structure and a method of forming a structure that includes a core made, at least in part, of a rice hull composition. The rice hull composition including a combination of separate, unground rice hulls; ground rice hulls; and a rice hull powder, that each have a different particle size. A polymeric binder, such as a recycled plastic polymeric binder binds the separated unground rice hulls, the ground rice hulls and the rice hull powder together.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.14/602,202, filed Jan. 21, 2015, issued as U.S. Pat. No. 9,937,642,which claims the benefit of U.S. Provisional Application No. 61/929,565,filed Jan. 21, 2014, both of which are incorporated in their entiretyherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This application relates generally to a method and apparatus involvingrice hulls and, more specifically, to construction panels and othermaterials formed at least in part of rice hulls and a method ofmanufacturing construction panels and other materials.

2. Description of Related Art

It is estimated that millions of tons of rice hulls are generated as abyproduct of processing rough rice for consumption throughout the world.These rice hulls are made of materials that are very durable and can bedifficult to recycle or otherwise dispose of. As a result, riceprocessors are often willing to give the rice halls to anyone willing totake them free of charge.

BRIEF SUMMARY OF THE INVENTION

According to one aspect, the subject application involves method offorming a structure including rice hulls. The method includes combiningseparated rice hulls, ground rice hulls and a rice hull powder that eachhave a different average particle size. A binder is used to bind theseparated rice hulls, the ground rice hulls and the rice hull powdertogether to form a rice hull composition. The binder includes apolymeric binder, preferably a recycled plastic polymeric binder. Therice hull composition is introduced to an extruder to form a rice hullextrudate. The extruder is pre-heated to a temperature from about 270°F. to about 450° F. The precise preheat temperature, which is the sameor different than the working temperature, will vary depending on thebinder to be used. For example, the preferred extruder temperature whenemploying a polypropylene binder is about 425° F. A compositionemploying a polyethylene terephthalate binder would be less than that ofpolypropylene. The rice hull extrudate can be molded into a desiredshape by pressing the rice hull extrudate into a mold having a cavitythat defines a desired shape of the structure to be produced or byspreading the rice hull extrudate on a conveyor belt with appliedpressure. After shaping, the rice hull extrudate is cooled to obtain thedesired structure.

According to another aspect, the subject application involves a buildingstructure that includes a core formed, at least in part, from a ricehull composition. The rice hull composition includes a combination ofseparate unground rice hulls, ground rice hulls and a rice hull powdereach having a different average particle size. The core also includes apolymeric binder binds the separated unground rice hulls, the groundrice hulls and the rice hull powder together.

The above summary presents a simplified summary in order to provide abasic understanding of some aspects of the systems and/or methodsdiscussed herein. This summary is not an extensive overview of thesystems and/or methods discussed herein. It is not intended to identifykey/critical elements or to delineate the scope of such systems and/ormethods. Its sole purpose is to present some concepts in a simplifiedform as a prelude to the more detailed description that is presentedlater.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING

The invention may take physical form in certain parts and arrangement ofparts, embodiments of which will be described in detail in thisspecification and illustrated in the accompanying drawings which form apart hereof and wherein:

FIG. 1 shows an illustrative example of a door comprising a core formedfrom a rice hull composition;

FIG. 2 shows a cross-sectional view of the illustrative example of thedoor 14 taken along line 2-2 in FIG. 1;

FIG. 3 shows a sectional view of a countertop comprising a core formedat least in part from a rice hull composition;

FIG. 4 shows a sectional view of a structural insulated panel comprisinga single core formed at least in part from a rice hull composition;

FIG. 5 shows a sectional view of a structural insulated panel comprisinginsulation sandwiched between opposing cores, each of which being formedat least in part from a rice hull composition;

FIG. 6 shows a sectional view of a roof panel 26 including a pluralityof stacked cores formed at least in part from the rice hull compositiondescribed herein;

FIG. 7 schematically depicts an illustrative manufacturing assembly formanufacturing the cores described herein when employing an urethanebinder;

FIG. 8 is a flow diagram schematically depicting a method of forming acore when employing an urethane binder;

FIG. 9 is a sectional view of a portion of a hollow core comprising aplurality of air-filled apertures or pockets;

FIG. 10 shows another embodiment of a core molded into the shape of abuilding block;

FIG. 11 shows an edge-alignment feature provided to plank-shaped coresto establish proper alignment of laterally-aligned cores; and

FIG. 12 shows another alignment feature provided to plank-shaped coresto establish proper alignment of overlapping cores.

FIG. 13 is a flow diagram schematically depicting another method offorming a core when employing a polymeric binder.

FIG. 14 schematically depicts an illustrative manufacturing assembly forforming the structures described herein when employing a polymericbinder.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used herein for convenience only and is not to betaken as a limitation on the present invention. Relative language usedherein is best understood with reference to the drawings, in which likenumerals are used to identify like or similar items. Further, in thedrawings, certain features may be shown in somewhat schematic form.

It is also to be noted that the phrase “at least one of”, if usedherein, followed by a plurality of members herein means one of themembers, or a combination of more than one of the members. For example,the phrase “at least one of a first widget and a second widget” means inthe present application: the first widget, the second widget, or thefirst widget and the second widget. Likewise, “at least one of a firstwidget, a second widget and a third widget” means in the presentapplication: the first widget, the second widget, the third widget, thefirst widget and the second widget, the first widget and the thirdwidget, the second widget and the third widget, or the first widget andthe second widget and the third widget.

Mounting pressure on the construction industry to conserve productscomprised of natural wood as well as the failure of traditional buildingmaterials to meet the evolving performance requirements of the marketplace has driven the investigation of new materials and manufacturingprocesses to develop such materials for use in the constructionindustry. The utilization of rice hulls in such construction materialsoffers the opportunity to recycle industrial by-product waste whileproviding a product such as construction panels, for example, withdesirable insulating qualities, resistance to burning, ease ofinstallation, resistance to insects, and enhanced strength relative toconventional building materials such as natural wood.

A matrix of resin, adhesives, rice hulls and optionally ground particlesand/or reinforcing fibers are compression molded into a desired shapewith heat to form panels having a core with desired and varying shapes,dimensions, forms and features. The resulting items created can have atleast one of the following attributes; resistance to moisture, fire,insects while providing structural strength against racking and shearforces. Items also provide quality characteristics including; thermalinsulation, sound deadening, strength to resist bending force and becomea stable substrate to support composite coatings, veneers and integralstructural members (such as wood rails and stiles). Items can beconstructed to form interlocking components that form a monolithicstructure such as wall sections and corners, for example. Of course anydesired construction paneling or other object can be formed, including,ceiling tiles, doors, etc. . . .

FIG. 1 of the present application shows an embodiment of a door 14comprising a core 10 (FIG. 2) formed, at least in part, from a rice hullcomposition. Embedded in the core 10, can optionally be one or morehardware mounting substrates 16 (shown in broken lines in FIG. 1)fabricated from wood, a synthetic plastic material, metal, or any othermaterial with sufficient rigidity and strength to withstand the forcescommonly exerted on such hardware. For example, the hardware mountingsubstrates 16 in FIG. 1 include a substrate arranged at a location wherea door handle and/or locking mechanism is to be installed, as well asone or more substrates along the hinged side 18 of the door 14 formounting hinge plates using threaded fasteners such as screws, forexample.

FIG. 2 shows a cross-sectional view of the illustrative example of thedoor 14 taken along line 2-2 in FIG. 1. The door 14 includes a core 10formed, at least in part, from a rice hull composition, optionally incombination with other building materials such as a binder, pigment orother coloring agent, and externally-exposed coating. In FIG. 2, theother building material includes a wood veneer skin 12 adhesivelyapplied to opposite exposed surfaces of the core 10. The wood veneerthus provides the door 14 with the external appearance of wood, whilethe core 10 provides the door 14 with the structural propertiesdescribed herein.

Although shown and described herein as a door 14 for the sake of brevityand clarity, the construction panel of the present application can beformed as any desired construction material that includes the core 10,such as a countertop 19, a cross-section of which is shown in FIG. 3.For example, rather than the wood veneer 12 shown in FIG. 2, acountertop material 20 (e.g., granite, marble, other tile, formica,Corian®, etc. . . . ), reinforcing structures, and the like can beprovided to the core 10 to form an externally-exposed countertopsurface.

As another example, a cross-sectional view of an embodiment of theconstruction panel in the form of insulated wall sheathing or structuralinsulated panel (“SIP”) 22 utilizing the core 10 comprising the ricehull composition. As shown, the SIP 22 includes the core 10 adheredagainst a rigid layer of insulation 24 such as foamed polystyrene, forexample. Alternate embodiments of the SIP 22 can include the The SIP 22can be manufactured under factory controlled conditions and can bestructurally configured to fit nearly any building design. Although onlya single layer of the core 10 is shown in FIG. 4, other embodiments ofthe SIP 22 can include a second layer of the core 10 arranged on anopposite side of the insulation 24 relative to the core 10 shown in FIG.4. In other words, the insulation 24 can optionally be sandwichedbetween opposing cores 10 as shown in FIG. 5.

FIG. 6 shows another illustrative embodiment of the construction panelin the form of a roof panel 26 including a plurality of stacked cores 10formed at least in part from the rice hull composition described herein.The stacked cores 10 are coupled together, and to an underlying framesuch as a truss or floor joists, for example, by a nail 28 or othersuitable mechanical fastener driven through the cores 10. A laminate,veneer 30, or other suitable coating material can optionally be appliedto the externally-exposed surface of the stack of cores 10.

The core 10 described herein comprises a rice hull composition thatincludes a rice hull composition formed from at least one of, andoptionally a combination of two or more of: separate unground ricehulls, ground rice hulls and a rice hull powder. Each of the separatedunground rice hulls, the ground rice hulls and the rice hull powdercomprises a different particle size, with the unground rice hulls havingthe largest particle size, and the rice hull powder having the smallestparticle size. The ground rice hulls, with an intermediate particlesize, can optionally be ground to a 16/80 mesh or to a minus 80 mesh toobtain a powdered rice hull product. According to a specific embodiment,the rice hull composition can include at least the unground rice hullsand the ground rice hulls.

A caustic-free polyurethane resin thermosetting binder can be combinedwith the rice hull composition to bind the separated unground ricehulls, the ground rice hulls and the rice hull powder together. Forexample, the binder can be a thermosetting material such as an aliphaticpolyurethane resin, optionally with a UV resistant component added toresist discoloration as a result of exposure to ultraviolet light. TheUV resistant material can also optionally protect the coloring agentagainst degradation by blocking at least a portion of ultraviolet lightimpinging on the core 10.

While urethane binders are useful and impart advantageous properties tothe rice hull composition, they can also be difficult to work with.Because they are sticky, use of urethane binders generally requiresinclusion of a releasing agent. They are also slow to cure and theentire composition (rice hulls and urethane) must be heated through inorder to fully cure the composition. An activator can be added to thecomposition in order to speed up the polymerization of the binder afterit is added to the rice hull mixture. In this regard, a ⅛″ thickstructure might take 2 minutes to fully heat and cure; a 2″ thickstructure might take 12-14 minutes to fully heat and cure. Once heatedand cured, the composition must also be given adequate time to cooldown. This slow production may limit the practical usefulness of theurethane binder and processes for using such in large-scalemanufacturing processes.

Thus, the rice hull composition of the present disclosure can alsoemploy other binders, such as pre-polymerized polymeric binders. Suchpre-polymerized polymeric binders, also referred to herein as polymericbinders, have been polymerized prior to their addition to the rice hullcomposition. Therefore, the curing step required when using binders suchas urethane can be avoided. Polymeric binders according to the presentdisclosure preferably comprise one or more types of plastics. Asdescribed in greater detail below, compositions employing a polymericbinder can be made by an extrusion process. That is, the rice hullcomposition and the polymeric binder can be mixed together, without theneed for activators or a release agent, and put through an extruderwhich heats the composition comprising rice hulls and the polymericbinder as it is pushed through the mold and/or die. The result is aproduct that cools rapidly regardless of the thickness. For example, a⅛″ thick structure or a 2″ thick structure might both cool in 1-3minutes. The result is a faster process that does not depend onstructure thickness, thereby improving the manufacturing process.

In one embodiment, the polymeric binder comprises polyethylene, highdensity polyethylene, low density polyethylene, polypropylene,polyethylene terephthalate, nylon, Teflon, polystyrene, acrylonitrilebutadiene styrene, fiber-reinforced plastic, or combinations thereof. Ina preferred embodiment, the polymeric binder can be obtained fromrecycled plastic products. In this regard, the recycled product is awaste product. That is, the use of a polymeric binder can incorporatematerial that would otherwise go into a landfill. This, of course,improves the environmentally friendliness of the structures describedherein. In a preferred embodiment, the polymeric binder comprisesrecycled plastic comprising polyethylene, high density polyethylene, lowdensity polyethylene, polypropylene or combinations thereof. In aparticularly preferred embodiment, the recycled plastic comprisespolypropylene. The recycled plastic material for use according to thepresent disclosure is preferably in the form of pellets of varying sizesresulting from any standard manufacturing process. The use of differentplastic binders, alone or in combination with other plastic polymericbinders, or with other non-polymeric binders, such as urethane, alsoallows the manufacturer to adjust the properties of the finalcomposition, such as the flexibility or rigidity of the final product,the strength, durability, UV absorbance or protection, and/or fireresistance of the final structure.

In addition to the rice hull composition and the binder, the materialforming the core 10 can also optionally include crumb rubber, which isparticular rubber derived from grinding, chopping, crushing or otherwisebreaking apart recycled tires. The crumb rubber included in the materialforming the core 10 can have an average particle size of approximatelyfour one-thousandths (0.004 in.) of an inch or less.

A manufacturing assembly for manufacturing the core 10 when employing aurethane binder is schematically illustrated in FIG. 7. Raw rice hulls32 are heated to any temperature within the range from approximately150° F. to approximately 500° F., (e.g., 150° F. for the presentembodiment), and combined with at least one of: polymeric fibers 34 suchas polyethylene terephthalate (“PET”), the ground rice hulls 36, therice hull powder, the heated binder 38, a pigment 40 for providing theend product with a desired color, and optional fire and/or smokeretardant material 42. This combination can optionally be introduced toa rotary mixer 44 to promote complete coverage of all of the rice hullparticulates with the binder 38. The selected components are mixed, andsubsequently dispensed into the appropriate mold 46 for the panel underconstruction. The quantities dispensed can be specifically-measuredquantities, and can optionally be included on, or surround a structuralre-enforcement such as a reinforcing mesh 48 in the heated mold 46. Amore detailed description of the method of forming a core 10 comprisingrice hulls employing a urethane binder is described with reference tothe flow diagram of FIG. 8. According to such a method, the separatedrice hulls, ground rice hulls and the rice hull powder, each having adifferent (and progressively smaller) particle size, are combined atstep S100. The combination of each type of rice hull material can takeplace in the mixer 44 shown in FIG. 7. The binder 38 is introduced tothe mixer 44 to bind the separated rice hulls, the ground rice hulls andthe rice hull powder together to form the rice hull composition at stepS110, as is the optional coloring agent at step S120. The mixtureincluding the rice hull composition is then introduced, at step S130, tothe heated mold 46 having a cavity that defines the desired shape of thestructure to be produced. While in the mold 46, the rice hull mixturecan be exposed to a temperature within a range from approximately twohundred (200° F.) degrees Fahrenheit to approximately two hundred eighty(280° F.) degrees Fahrenheit, and optionally within a range fromapproximately two hundred forty (240° F.) degrees Fahrenheit toapproximately two hundred fifty (250° F.) degrees Fahrenheit. However,according to other embodiments, the rice hull composition within themold can be heated in an environment having any temperature within arange from approximately one hundred fifty (150° F.) degrees Fahrenheitto approximately five hundred (500° F.) degrees Fahrenheit withoutdeparting from the scope of the present disclosure. The rice hullmixture in the mold 46 can also be subjected to a molding pressurewithin a range from approximately two hundred (200 psi) pounds persquare inch to approximately two thousand (2,000 psi) pounds per squareinch. Exposure of the rice hull composition to the elevated temperatureand pressure can continue for a time within a range from approximatelytwo (2 min.) minutes to approximately six (6 min.) minutes, depending onthe size of the core 10 being manufactured.

The heat from the mold or other heat source at step S130 initiatescuring of the thermosetting binder to initially fix the shape of therice hull composition in the shape of the mold 46. However, before thebinder has fully cured, the rice hull composition is removed from themold at step S140, to be subsequently subjected to another elevatedtemperature to complete curing of the binder externally of the mold 46at step S150. Once the rice hull composition has been fully cured, therice hull composition can be combined with an exposed surface structuresuch as the wood veneer or countertop surface, for example, or othermaterial described herein at step S160. Examples of other suitablesurface structure materials include, but are not limited to, at leastone of: a re-enforced polyethylene terephthalate; asubstantially-transparent polyurethane coating; and a waterborne acrylicurethane material.

Alternatively, a more detailed description of the method of forming acore 10 comprising rice hulls employing a polymeric binder is describedwith reference to the flow diagrams of FIG. 13 and FIG. 14. According tosuch a method, when the structure is made comprising the plastic binder83 as set forth above, the separated (whole) rice hulls 80, ground ricehulls 81 and the rice hull powder 82, each having a different (andprogressively smaller) particle size, are combined together at step S200with the polymeric binder 83 in a dry mixer or tumble mixer 90. Theunground rice hull can be present in an amount of from 1% to 98% w/wrelative to the weight rice hull mixture. Likewise, the ground rice hulland powdered rice hull can also be present in an amount of from 1% to98% w/w relative to the weight of the rice hull mixture. Preferably, inone embodiment of the composition disclosed herein, the rice hullmixture comprises from 20% to 50% w/w of each of the unground rice hull,the ground rice hull and the rice hull powder. In a particularlypreferred embodiment, the rice hull mixture comprises about 33% w/w ofeach of the unground rice hull, the ground rice hull and the rice hullpowder. The polymeric binder 83 is preferably in the form of pelletsresulting from any standard plastics recycling process. The amount ofthe binder present in the rice hull composition can vary from about 1%to about 30% w/w relative to the weight of the rice hull mixture.Preferred embodiments of the composition include from about 10% to about25%, from about 12% to about 20% or about 15% w/w of binder relative tothe weight of the rice hull mixture.

Optionally, re-enforcing fibers 34, can be added to the dry mixer 90 ifdesired, as can be crumb rubber, and/or fire and/or smoke retardantmaterial, as described herein. Once a homogeneous mixture is formed, therice hull mixture is introduced to an extruder 91 in step S210. The hotextrusion process thermomechanically transforms raw materials, such asthe rice hull mixture described herein, in short time and hightemperature conditions under pressure. The process forces a materialthough a die or an orifice to form a shape. The material is firstsoftened (plasticization) by heating so that it can be shaped. A screw(single or twin screws) forces the material towards, and then through, adie. Shape can be imparted by the die, or by post-extrusion forming(shaping outside of the extruder prior to cooling). The product is thencooled to set the desired shape and obtain the finished product 100.

In the present method, the extruder 91 is pre-heated to a temperature offrom about 270° F. to about 450° F., preferably between about 350° toabout 390° F., or preferably about 425° F. After passing through theextruder 91 in step S220, a rice hull extrudate 85 comprising of the hotrice hull mixture having an oatmeal-like consistency is then molded inone of two ways.

For smaller molded items, in step S230, the hot rice hull extrudate 85is forced into a mold form 92, preferably a metal mold form, of adesired shape. The mold form can be optionally heated to or near to thetemperature of the extruder. The mold 92 can optionally include coolingchannels through which cold water is passed to draw the heat from therice hull extrudate 85 in order to cool it. The rice hull extrudate 85in the mold 92 can be subject to an applied pressure 93 varying frombetween about 200 psi to about 1700 psi, depending on the requirementsof the finished part 100, to ensure that the rice hull extrudate 85fully fills the mold form 92. Once the mixture is cooled to roomtemperature in the mold 93 in step S240, the finished part 100 is set inits desired shape and can be removed from the mold 93 in step S250.

Alternatively, for larger molded items, a continuous forming process maybe desired. In a continuous forming process, the rice hull extrudate 85is first spread upon a bottom conveyor belt 94 at step S260, and in stepS270 pressure (about 200-1700 psi) is applied from a second conveyorbelt 95 above to thin the rice hull extrudate 85 to a desired averagethickness, for example, of from about ⅛ of an inch to 3 inches, or fromabout ¼ of an inch to 2 inches, or about 7/16 of an inch. In step S280,the bottom conveyor belt 94 moves the rice hull extrudate 85 through acooling chamber 96 to speed the cooling process. Due to the size and themass of these larger finished products 100, such as sheets of the ricehull composition, large cores 10, or other large desired shapes, thefinished part 100 must fully cool before it is removed from the systemin step S290.

The resulting core 10 can possess characteristics desirable in the fieldof construction. For instance, a moisture test conducted on such a panelrequired the panel to be fully submerged in water at room temperaturefor four (4 mos.) months. The panel exhibited less than a five (5%)percent weight gain over the duration of the test. The weight gain wasapproximately four (4%) percent, by mass. The rate at which the panelgained water weight also appeared to slow over time. Of theapproximately four (4%) percent weight gain realized over the four monthspan, the panel exhibited an approximately three (3%) percent weightgain during the first week of the test.

The core 10 formed from the rice hull composition can be formed as asolid object, or optionally as defining a plurality of air-filledapertures 50 or pockets as shown in FIG. 9. Although the apertures 50are shown in a linear arrangement in FIG. 9, any desired pattern ofapertures 50 can optionally be adopted. For example, another embodimentof the core 10 can optionally include a honeycomb arrangement ofapertures 50 without departing from the scope of the present disclosure.

Also, rather than being formed in a planar shape as a plank, the corecan be molded into any desired shape. Another embodiment of the core 10including air-filled voids is illustrated in FIG. 10, and forms abuilding block that can be assembled adjacent to a plurality of othersuch blocks to construct a foundational wall for example. As shown inFIG. 10, the core 10 includes parallel and opposing planar side walls 56separated by air-filled apertures 50 established during the moldingprocess. Similarly, parallel and opposing end walls 58 are integrallyformed as monolithic structures with the side walls 56 on oppositelongitudinal ends of the block-shaped core 10. One, or a plurality oftransverse partitions 60 can be formed between the end walls 58 toestablish a plurality of apertures 50.

The external surface of each core 10 within a region adjacent to one orboth end walls 58 can optionally include an alignment feature 62. Thealignment feature 62 of each core 10 is cooperable with a similaralignment feature provided to an abutting core arranged adjacent to thecore 10 as part of an assembly. Cooperation between the alignmentfeature 62 can establish a substantially-linear arrangement of theabutting cores 10, or a substantially-perpendicular arrangement, forexample. In the embodiment appearing in FIG. 10, the alignment feature62 includes vertical spines 64 separated by vertical troughs 66. Thespines 64 and troughs 66 on each core can be configured such that thespines 64 of a first core 10 are received in the troughs 66 of theadjacent core provided to the end wall 58 to promote a lineararrangement of those cores 10. Similarly, spines 64 and troughs 66 oneach core can be configured such that the spines 64 provided to the endwall 58 of a first core are received in the troughs 66 of the adjacentcore provided to the side wall 56 to promote a perpendicular arrangementof those cores 10, thereby forming a corner.

In addition to the block-shaped cores 10, the cores 10 formed as plankscan also include alignment features for being joined with neighboringplanks. For example, each plank formed of the rice hull compositiondescribed herein can include an overhang 70 along one longitudinal edgeof the plank, as schematically shown in FIG. 11. For the plank on theright in FIG. 11, the overhang extends laterally outward from an upperregion of the plank. A similarly-configured core 10, on the left in FIG.11, is oriented so the overhang 70 extends laterally outward from thelower region of the plank and arranged such that the overhangs 70 ofeach plank overlap to form a lap joint. Although the overhangs 70 inFIG. 11 extend from the upper or lower region of the plank, depending onthe plank's orientation, other embodiments can utilize a tongue andgroove configuration. For such embodiments, the tongue extending alongone lateral side of the plank is adapted to be received in a troughformed in the opposite lateral side of an adjacent plank, again ensuringproper alignment of the adjacent planks.

Another embodiment of the alignment feature provided to plank-shapedcores 10 is shown in FIG. 12 as a keyed joint. As shown, each plankincludes a protrusion 72 from an upward-facing major surface 74 and asimilarly-located recess 76 (shown using hidden lines) formed in adownward-facing major surface 78. Planks placed on top of each other canbe properly aligned through cooperation of the protrusion 72 and therecess 74 formed in the overlaid plank.

Regardless of their physical shape, the resulting cores can have thefollowing properties:

Densities as low as 20 lbs. per cubic foot and as high as 108 lbs. percubic foot;

Thermal resistance with an R-value of 1.7 for a 1.66 inch thick plank;

Ballistic resistance—1.25 in. thick planks were shot with a .22-cal.Bullet at a range of 6″. The projectile entered the core of rice hullcomposition shaped as a plank, but did not exit the plank.

In addition to the moisture resistance, the construction panelsdescribed herein also exhibit desirable mechanical characteristics anddurability. For example, the experimental results outlined below reflectthe tear strength of various samples.

Experimental I

TABLE 1 Tear Strength of Example 1 Thickness (in.) Tear Strength(lbs/in.) 1 0.197 202.073 2 0.197 160.501 3 0.185 247.145 4 0.205273.378 5 0.197 300.203 Mean 0.196 236.660 Standard Deviation (SD) 0.00755.885 Mean + 2SD 0.210 348.429 Mean − 2SD 0.182 124.890

Experimental II

TABLE 2 Tear Strength of Example 2 Thickness (in.) Tear Strength(lbs/in.) 1 0.207 498.902 2 0.207 184.732 3 0.039 2000.148 4 0.197272.502 5 0.181 236.804 Mean 0.166 638.618 Standard Deviation (SD) 0.072770.518 Mean + 2SD 0.309 2179.654 Mean − 2SD 0.023 −902.419

Experimental III

TABLE 3 Tear Strength of Example 3 Thickness (in.) Tear Strength(lbs/in.) 1 0.039 609.885 2 0.177 58.854 3 0.197 138.578 4 0.197 160.8705 0.177 109.288 Mean 0.157 215.495 Standard Deviation (SD) 0.067 223.752Mean + 2SD 0.291 662.999 Mean − 2SD 0.024 −232.009

Experimental IV

TABLE 4 Tear Strength of Example 4 Thickness (in.) Tear Strength(lbs/in.) 1 0.197 184.728 2 0.197 149.045 3 0.217 434.020 4 0.197384.482 5 0.217 514.219 Mean 0.205 333.299 Standard Deviation (SD) 0.011159.311 Mean + 2SD 0.226 651.920 Mean − 2SD 0.183 14.678

Experimental V

TABLE 5 Tear Strength of Example 5 Thickness (in.) Tear Strength(lbs/in.) 1 0.201 928.718 2 0.205 1174.824 3 0.197 508.455 4 0.197752.462 5 0.187 536.348 Mean 0.197 780.161 Standard Deviation (SD) 0.007279.224 Mean + 2SD 0.210 1338.609 Mean − 2SD 0.184 221.713

Experimental VI

TABLE 6 Tear Strength of Example 6 Thickness (in.) Tear Strength(lbs/in.) 1 0.226 944.090 2 0.226 570.524 3 0.197 397.608 4 0.205235.871 5 0.205 402.784 Mean 0.212 510.176 Standard Deviation (SD) 0.014269.894 Mean + 2SD 0.239 1049.963 Mean − 2SD 0.184 −29.612

Illustrative embodiments have been described, hereinabove. It will beapparent to those skilled in the art that the above devices and methodsmay incorporate changes and modifications without departing from thegeneral scope of this invention. It is intended to include all suchmodifications and alterations within the scope of the present invention.Furthermore, to the extent that the term “includes” is used in eitherthe detailed description or the claims, such term is intended to beinclusive in a manner similar to the term “comprising” as “comprising”is interpreted when employed as a transitional word in a claim.

What is claimed is:
 1. A structure comprising: a core comprising a ricehull composition formed from a combination of separate unground ricehulls, ground rice hulls and a rice hull powder, wherein the separatedunground rice hulls, the ground rice hulls and the rice hull powder eachcomprises a different particle size; and a polymeric binder that bindsthe separated unground rice hulls, the ground rice hulls and the ricehull powder together.
 2. The structure of claim 1 wherein the polymericbinder is selected from the group consisting of polyethylene, highdensity polyethylene, low density polyethylene, polypropylene,polyethylene terephthalate, nylon, Teflon, polystyrene, acrylonitrilebutadiene styrene, fiber-reinforced plastic, and combinations thereof.3. The structure of claim 2, wherein the polymeric binder comprisesrecycled material.
 4. The structure of claim 3, wherein the polymericbinder comprises a recycled material selected from the group consistingof recycled polyethylene, recycled high density polyethylene, recycledlow density polyethylene, recycled polypropylene and combinationsthereof.
 5. The structure of claim 1, wherein the structure has anaverage thickness of from about ⅛ of an inch to about 3 inches.
 6. Thestructure of claim 5, wherein the average thickness is about 7/16 of aninch.
 7. The structure of claim 1, the rice hull powder comprising anaverage particle size of 16/80 mesh.
 8. The structure of claim 1 furthercomprising a coloring agent distributed throughout the rice hullcomposition.
 9. The structure of claim 1 further comprising crumb rubberhaving an average particle size of approximately four one-thousandths(0.004 in.) of an inch or less combined with the rice hull composition.10. The structure of claim 1 further comprising an externally-exposedsurface comprising at least one of: a re-enforced polyethyleneterephthalate; a substantially-transparent polyurethane coating; and awaterborne acrylic urethane material.
 11. The structure of claim 1further comprising a re-enforcing structure embedded within rice hullcomposition of the core.
 12. The structure of claim 1, wherein the corecomprises a plurality of joined segments, and each of the joinedsegments comprises the core comprising the rice hull composition. 13.The structure of claim 1, wherein the core comprises network ofair-filled voids.
 14. The structure of claim 13, wherein each of theair-filled voids is open to an ambient environment.
 15. The structure ofclaim 14, wherein the core comprises and end region, and anexternally-exposed surface of the core comprises an alignment featurearranged adjacent to a terminal edge of the core, the alignment featurebeing cooperable with an alignment feature provided to an abutting corearranged adjacent to the core as part of an assembly.
 16. The structureof claim 1, wherein the process for manufacturing the structurecomprises the steps of: combining the separated rice hulls, ground ricehulls, the rice hull powder, and the polymeric binder in a dry mixer toform a rice hull composition; introducing the rice hull composition toan extruder to form a rice hull extrudate, wherein the extruder ispre-heated to a temperature of from about 270° F. to about 450° F.;molding the extrudate to a desired shape and cooling the desired shapeto obtain the structure.